How to generate a category tree

public class Category
{
    public int Id { get; set; }

    public Thread Thread { get; set; } = null!;
    public Guid ThreadId { get; set; }

    public string Name { get; set; } = string.Empty;
    public string Title { get; set; } = string.Empty;
    
    public ICollection<Category> Subcategories { get; set; } = new List<Category>();
    public int? CategoryId { get; set; }
}

public class Category
{
    public int Id { get; set; }

    public Thread Thread { get; set; } = null!;
    public Guid ThreadId { get; set; }

    public string Name { get; set; } = string.Empty;
    public string Title { get; set; } = string.Empty;
    
    public ICollection<Category> Subcategories { get; set; } = new List<Category>();
    public int? CategoryId { get; set; }
}